Elemental analyses were obtained from two different clones of Trypanosoma Cruzi (a pathogenic protozoan causing Chagas' disease) that had previously been shown to have differences in their virulence and optical properties. The analyses was accomplished by means of elemental mapping in BEIB's computerized analytical electron microscope. Samples were prepared by rapidly freezing whole cells placed in an ammonium nitrate buffer and supported on formvar/carbon EM grids; samples were freeze-substitutes prior to analysis. X-ray maps of Fe, Zn, Mg, K, Ca, P, and S were recorded from a number of epimastigotes from each clone. Different iron contents were established for the two cell types, one clone having approximately twice the Fe content of the other, with most appearing to be in the mitochondrial region and possibly attributable to cytochromes. Other differences were seen in the amounts of divalent cations (Mg, Ca and Zn), which were mainly bound with phosphate in dense bodies scattered throughout the cells.